The present invention relates to a chemical mechanical polishing aqueous dispersion and a chemical mechanical polishing method.
In recent years, interconnects formed in semiconductor devices have been increasingly scaled down along with an increase in the degree of integration of semiconductor devices. In view of such a situation, a chemical mechanical polishing (hereinafter may be referred to as “CMP”) that planarizes various films (metal film and planarization sacrificial film) method that form a semiconductor device by utilizing a chemical effect and a mechanical effect has been used.
Specifically, a conductor metal (e.g., aluminum, copper, or tungsten) is deposited by sputtering, plating, or the like in a minute groove (hereinafter referred to as “via-hole”) formed in an insulating film (e.g., silicon oxide) formed on a semiconductor wafer. A metal film unnecessarily stacked around the via-hole is removed by CMP while allowing a metal to remain in the via-hole to obtain a planarized surface (see JP-T-2002-518845, for example). In particular, when forming interconnects of a high-performance integrated circuit, a minute interconnect structure is formed by CMP.
It is difficult to deposit a metal in a via-hole (i.e., fill the via-hole with a metal) in a minute interconnect area of a high-performance integrated circuit. Since tungsten has an excellent filling capability, tungsten has been used as a minute interconnect-forming material. As a polishing composition used to polish a wafer on which a tungsten film is formed, a polishing composition that contains an oxidizing agent (e.g., hydrogen peroxide), an iron catalyst (e.g., iron nitrate), and abrasive grains (e.g., silica) has been proposed (see JP-T-2005-518091, for example).
JP-T-2005-518091 describes that the pH of the polishing composition is 7 or less, preferably 3 to 6, and more preferably 3.5 to 5 (e.g., 4) when the polishing composition is used to polish a copper-containing material, is preferably 2 to 7 when the polishing composition is used to polish a platinum-containing material, is 5 or more, and preferably 7 to 11 when the polishing composition is used to polish a ruthenium-containing material, and is 5 to 12, and preferably 7 to 9 when the polishing composition is used to polish an iridium-containing material. However, since the above pH range of the polishing composition is not practical when the polishing composition is used to polish a tungsten-containing material, a flat polished surface cannot be obtained when polishing tungsten using the polishing composition having a pH within the above range.
Various performances (e.g., polishing rate, flatness, and scratch resistance) are required for a tungsten polishing composition. Along with a recent reduction in interconnect width, erosion (wear) that occurs in a minute interconnect area poses a problem with regard to flatness. It is considered that erosion occurs due to dishing (depression) that occurs in a tungsten interconnect area and thinning (wear) that subsequently occurs in silicon oxide positioned between the tungsten interconnects.
In order to solve the above problem, a highly selective polishing composition that polishes a tungsten film at a significantly high polishing rate as compared with a silicon oxide film and can polish a silicon oxide film to only a small extent, a nonselective polishing composition that polishes a tungsten film and a silicon oxide film at an almost identical polishing rate, and the like have been proposed. However, since the highly selective polishing composition has a strong effect on a tungsten film, a deterioration in flatness (dishing) may occur in a wide interconnect area, or the surface of the tungsten film may be roughened, for example. On the other hand, since the nonselective polishing composition does not achieve nonselectivity at a high polishing rate, the polishing rate must be decreased. In this case, the polishing time of a tungsten film-deposited patterned wafer increases.